Create HiresImageSaveChooser and Rename statusbar

[cjmayo]

A couple of tweaks:

• Create a HiresImageSaveChooser class to be consistent with all the other file choosers in ApplicationDialogs
• Rename ApplicationWindow.bar to statusbar, clarifying what it is and matching menubar and toolbar

[codecov[bot]]

Codecov Report

Merging #230 (9534e49) into master (544bfd5) will decrease coverage by 0.00%. The diff coverage is 95.45%.

@@            Coverage Diff             @@
##           master     #230      +/-   ##
==========================================
- Coverage   85.97%   85.96%   -0.01%     
==========================================
  Files          57       57              
  Lines       10411    10413       +2     
==========================================
+ Hits         8951     8952       +1     
- Misses       1460     1461       +1     

Impacted Files	Coverage Δ
fract4dgui/application_widgets.py	90.56% <92.30%> (+0.24%)	:arrow_up:
fract4dgui/application_window.py	89.18% <100.00%> (-0.52%)	:arrow_down:
fract4dgui/main_window.py	63.88% <100.00%> (ø)

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